Types of biodiversity
There are four types of biodiversity
• It is the diversity of genes within a species. There is a genetic variability among the populations and the individuals of the same species.
• Genetic diversity within a species increases with environmental variability.
• The genetic makeup of a species is not static, it changes as a result of internal and external factors. This variable genetic makeup of a species enables a species to evolve by means of natural selection. A species inhabiting a broad area and interbreeding throughout the whole area has high rate of gene flow and shows a few or no localised characters. However, a species living in a small or isolated area has low rate of gene flow and, as it adapted over time to a particular environment, develops into a distinct localised population.For More Biology Doubts check out our biology doubts section.
• Genetic variations are produced in populations of organisms that can reproduce sexually, by genetic recombinations and gene or chromosomal mutations. The genetic variation in interbreeding population is regulated by selections. Selection leads to certain genetic attributes being preferred and results in changes in the frequency of genes within the gene pool. The differences in the genetic pool in the amount and distribution are due to the variation in the complexity of habitats. It is estimated that there are 1010 different genes distributed across the world’s biota. The genes that control the fundamental biochemical processes are conserved across different species and show little variations. Specialised genes display a greater degree of variations.
It is the diversity among species in an ecosystem. Species are the distinct units of the biodiversity. Each species plays a specific role in an ecosystem. Species diversity refers to the variety of species within a region. ‘Biodiversity hotspots” are excellent examples of species diversity.
Whittaker described three common indices used to measure species-level biodiversity.
i) Species richness- Species evenness
- Species richness is the simplest measure of biodiversity. Species richness is the number of species per unit area. Greater the species richness, greater is the diversity. However the number of individuals among species may vary resulting in the differences in the species evenness. The species richness increases from high latitudes to the low latitudes. However the peak of the species richness is not at equator, but between 20- 30°N. The level of species richness increases rapidly from the north region to the equator but decreases slowly from the equator to southern region. At lower latitudes, area is large, solar radiation and resources like minerals and water are more, hence higher levels of species richness. Larger area is more topographically and environmentally diverse, therefore, higher species diversity at lower latitudes.
- Most times, the levels of endemism and that of species richness are positively correlated. In some oceanic islands, there are high levels of endemism but the levels of species richness are quite low. If in an area three species of birds are present, with two species represented by one individual each and the other represented by four individuals, the sample area is with lesser evenness. If the same area is with three species, each species is with two individuals, the sample area is with greater evenness. The chance of each species represented in a sample is greater in this area; hence this area is more diverse than the earlier. If a sample area is with two elephants, two insects and two birds, this area is most diverse as it has taxonomically unrelated species. In nature both types or kinds of species as well as the number of individuals per species vary, leading to changes in species diversity.
- Species richness is an incomplete measure of diversity and has limitations when it comes to comparing the diversity of two different sites, areas or countries.
- Species evenness is a diversity index, a measure of biodiversity which quantifies ho’ equal the populations are numerically. So if there are 40 foxes, and 1000 dogs, the population is not very even. But if there are 40 foxes and 42 dogs, the population is quite even. The evenness of a population can be represented by Pielou’s evenness index:
Where is the number derived from the Shannon-Weiner diversity index and is the total number of species found.
ii) Simpson index
Simpson’s species diversity index is used to quantify the biodiversity of a habitat. It takes into account the number of species present, as well as the relative abundance of each species. It represents the probability that two randomly selected individuals in the habitat belong to the same species.
The formula for the Simpson index is:
Where N is the total number of organisms of different species and n,is the number of organisms of a species.
iii) Shannon weiner index
It takes into account the number of species and the evenness of the species. The index is increased either by having more unique species, or by having greater species evenness.
III. Ecosystem diversity
It is the diversity at a higher level of organization. There are three other indices which are used by ecologists:
i) Alpha diversity: Alpha diversity refers to diversity within a particular area, community or ecosystem, and is measured by counting the number of taxa within the ecosystem.
ii) Beta diversity: Beta diversity is species diversity between ecosystems; this involves comparing the number of taxa that are unique to each of the ecoystems.
iii) Gamma diversity: Gamma diversity is a measure of the overall diversity for different ecosystems within a region.
iv) Global diversity
The overall biodiversity of the Earth.
Biodiversity not only applies species, but also to their immediate environment i.e. biotope (an area that is uniform in environmental conditions and in its distribution of animal and plant life) and their larger ecoregion (an area constituting a natural ecological community with characteristic flora, fauna, and environmental conditions and bounded by natural rather than artificial borders). An ecozone or biogeographic realm is the largest scale biogeographic division of the earth’s surface based on the historic and evolutionary distribution patterns of plants and animals. Ecozones represent large areas of the earth’s surface where plants and animals developed in relative isolation over long periods of time, and are separated from one another by geologic features, such as oceans, broad deserts, or high mountain ranges, that formed barriers to plant and animal migration.